Fix the Bug of SONiC Extension Packages Migration

[PeterTSW-EC]

What I did

• SONiC updates the format of the CLI section in the manifest.json on 17/5/2023. (Link)
• The implementation was merged to master, 202311, or later branches. (Link)
• However, the PR #2753 Comment reported that an error occurred when the CLI migration.
• The root cause is occurred while a CLI field (show/config/clear) is empty ('').
• This PR corrects the manifest.json parser that leaves the empty list ([]) instead of a list with an empty string (['']) when the CLI field is empty ('').

How I did it

• Update the manifest.py, and add a condition that returns an empty list ([]) when the CLI field is an empty string (''); Otherwise, return a list with a single string path (['/xxx/xxx']).

How to verify it

Execute the command "sudo sonic-package-manager install -y --from-tarball ./docker-test.gz", or install a new version of the SONiC image. (It executes the "sonic-package-manager migrate" during the installation. )

Previous command output (if the output of a command-line utility has changed)

New command output (if the output of a command-line utility has changed)

[PeterTSW-EC]

The PR #2753's comment was mentioned about the same issue. This PR fixes the Issue #3425.